Method for increasing the strength of alloys



UNITED STATES PATENT OFFICE rmrnon roa mcamsmc rm: s'mnncrn OF ALLOYS New York No Drawing. Application Apr-I14, 1933, I Serial No. 664,449

a Claim' (01. 148-215) The present invention relates to a method for increasing the strength of alloys which are capable of being age hardened and consist substantially of iron, cobalt and metal from the 6th group' of Mendelejefis periodic table of elements. Such alloys, if desired, may contain relatively small 7 percentages of additional elements such as vanadium, manganese and carbon. Alloys of this character are well known and generally are em- 10 ployed as metal cutting tools such tools being par ticularly adapted for use in cutting steel.

Alloys of the above composition may be produced by casting the mixed ingredients into an alloy ingot which may be forged, rolled, pressed or otherwise treated as required in a manner similar to the treatment of high speed steels.

After this treatment the alloy is heated to a temperature between 1000 C. and 1500 C.,

quenched to about room temperature and then aged at a temperature between about 250 C. and

700 C. An alloy consisting for example of about 29.8% cobalt, 18.7% tungsten, 3.32 molybdenum,

1.85% vanadium, 0.16% manganese, 0.1% carbon, 0.1% chromium and the remainder iron after the above heat treatment has a Rockwell C hardness which may vary from about 63 to 69 and a transverse breaking strength varying from about 175,000 to 250,000 lbs. per square inch.

In carrying out the present invention, I employ an arrested quench. For example after the alloy.

has been heated at a temperature of about 1000 C. to 1500 C. for a relatively short period of time varying from a few minutes to about fifteen minutes, instead of quenching the alloy to room temperature as heretofore suggested, I quench it in a molten lead, salt or equivalent bath to a temperature between about 500 C. and 700 C.,

i. e. about 600 C. and then transfer'the alloy to a muille furnace heated to about 600 C. and

40 cool the alloy to a temperature below 300 C.,

which if desired may be room temperature, in

a period of time which may vary from about 111- teen minutes to six hours. The resulting product has a Rockwell C hardness of about 45 to 4'7 and 45 a transverse breaking strength of about 450,000

to about 520,000 lbs. per square inch.

When the alloy is quenched from a temperature of about 1200 C. in a lead bath having a temperatime of about 600 C., the temperature of the alloy 50 is reduced to the temperature of'the bath in a very short time, probably less than a minute since at the end of that time the alloy has substantially the same color as the lead bath. The transverse breaking strength of the alloy after quench- I 56 ing in the lead bath and cooling to approximately room temperature is about 100,000 lbs. greater than the strength of-a similar alloyquenched from a temperature of about 1200 C. to room temperature. Quenching the alloy from the heat treating temperature above 1000 C. to a tempera- 5 ture of about 600 C. prevents precipitation in the alloy of an excess hard compound between these temperatures while the slow cooling from 600 C. eifects an increase in strength of the alloy.

When the alloy has been cooled to room temw perature or to a temperature between room temperature and about 300 C., it may be aged at temperatures varying from about 250 to 700 C. The aging process increases the hardness of the alloy to about 63 to 69 on the Rockwell C scale 15 but at the same time efiects a slight reduction in the strength of the alloy. If the lower range of aging temperature is employed the increase in hardness of the alloy takes place very slowly, so that it is generally preferable to harden the alloy 20 at temperatures varying from about 500 to 650 C.

In carrying out my invention, alloys having the specific composition given above were quenched from 1275 C. into a salt bath at 600 0., held in the bath for about 1 minutes and then cooled 25 from 600 C. to room temperature in air or in lime in a period of time varying from about 15 minutes to' 3 hours. These alloys were then "age hardened by placing-them in a furnace heated to about 70 C. and the furnace temperature was 30 then increased to about 525 C. in aboutv 40 minutes. This temperature was maintained for approximately 15 minutes after which the alloys were removed and cooled to room temperature either in lime or in still air, the cooling period in lime being about three hours and the, cooling period in still air being about 15 minutes. These latter cooling rates are not important but should not be too rapid. The alloys so treated had a hardness of about 66 on the Rockwell C scale and a transverse breaking strength of about 340,000 lbs. per square inch which indicates that although the primary strength of such alloys is reduced during the age hardening process the secondary strength is still far above that obtained in alloys in which an arrested quench has not been employed.

Asa metal cutting tool material, I prefer to employ an alloy consisting substantially of about 15% to 35% cobalt, about 12% to 30% of metal from the 6th group of Mendelejefis periodic table of elements, an appreciable amount up to about 3% vanadium, an appreciable amount up to about 0.6% manganese and the remainder iron. The invention-however is not limited to this com-- consist substantially of iron, cobalt and tungsten,

or substantially of iron, cobalt. tungsten and vanadium within the limits indicated above and which are made either by casting or sintering the ingredients of the alloy. Although I prefer to employ my process with alloys which are substantially carbon free the presence of relatively small quantities of carbon does not interfere with the operation of the process.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of producing a strong alloy containing about 15% to 35% cobalt; about 12% to of metal of the sixth group of Men'delejefis periodic table of elements, the remainder consisting substantially of iron, which comprises heating the alloy to a temperature above 1000.

C. but not materially higher than 1500 C. quenching the alloy to a temperature between about 500 C. and about 700 C. and cooling the alloy at a relatively slow rate to room temperature.

2. The method of producing a strong alloy containing about 15% to cobalt, about 12% to 30% of metal of the sixth group of Mendele- Jeff's periodic table of elements, the remainder consisting substantially of iron, which comprises heating the alloy to a temperature above 1000 .C. but not materially higher than 1500 C.,

quenching the alloy to a temperature between about 500 C. and about 700 C., cooling the alloy at a relatively slow rate to a temperature between comprises heating the alloy to a temperature above 1000 C. but not materially higher than 1500 C., quenching the alloy in a bath having a temperature: of about 500 C. to 700 C., slowly cooling the alloy in aperiod of time varying from about fifteen minutes to six. hours ,to, a temperature between room temperature and 300 C., and then aging the alloy at a temperature between 250 C. and 700 C.

4. The method of producinga strong alloy consisting substantially of about 15% to 35% cobalt, about 12% to 30% of metal of the sixth group of Mendelejeifs periodic table of elements, a fractional quantity up to about 3% vanadium,

the remainder of the composition consisting subv stantially of iron, which comprises heating the alloy to a temperature above 1000 C. but not materially higher than 1500 C., quenching the alloy in a bath having a temperature of about 500 C. to 700 C. and slowly cooling the alloy to room temperature in a period of time varying from about fifteen minutes to about six hours.

5. ,The method of producing a strong alloy consisting substantially of about 15% to 35% cobalt, about 12% to 30% of metal of the sixth group of Mendelejefis periodic tableoi. elements, a fractional quantity up to about 3% vanadium, the remainder ofv the composition consisting substantially of iron, which, comprises heating the alloy to a temperature above 1000 C. but not materially higher than 1500 C., quenching the alloy in a bath having a temperature of about 500" C; to 700. C., cooling the alloy to room temperature in a period of time varying from about fifteen minutes to about six hours, and age hardening the alloy ,at a temperature between 250 C. and I00" C. l

6. The method of producing a strong alloy consisting substantially of about 15% to 35% cobalt, about 12% to 30% of metal from a group consisting of tungsten, molybdenum and chromium, a fractional quantity up to about 3% vanadium, a fractional quantity and up to about .6%' manganese, the remainder of the composition consistingsubstantially of iron, which comprises heating the alloy to a temperature above 1000 C. but not materially higher than 1500 C., quenching the alloy in a bath having a temperature of about 500 C. to 700 C., cooling the'alloy to room temperature in a period of time varying from about fifteen minutes to about six hours, and

age hardening the alloy at a temperature between 250 C. and 700 C.

- WESLEY P. SYKES. 

